Photo/Illutration Akira Ishiwatari and other officials with the Nuclear Regulation Authority inspect a fault on the grounds of the Shika nuclear power plant in October 2022. (Asahi Shimbun file photo)

Hokuriku Electric Power Co. has cleared a nagging safety hurdle in its long struggle to restart the No. 2 reactor of its Shika nuclear power plant in Ishikawa Prefecture in central Japan.

The Nuclear Regulation Authority on March 3 finally agreed with the utility’s contention that there was no active fault running under the reactor. The existence of an active fault would have meant the reactor would have to be mothballed.

Hokuriku Electric applied in August 2014 for resumption of operations at the No. 2 reactor, but an NRA panel of experts the following year concluded that the possibility of an active fault under the reactor could not be ruled out.

That put the ball in the utility’s court to demonstrate that no active fault existed.

The measure was part of stricter safety regulations that the NRA put in place after the 2011 Great East Japan Earthquake and tsunami.

The NRA's definition of an active fault is in which seismic activity that had occurred from between 120,000 and 130,000 years ago cannot be ruled out.

At the March 3 NRA screening session, Hokuriku Electric officials provided data showing that for 10 faults there were soil layers where sedimentation had occurred prior to 120,000 to 130,000 years ago.

The NRA concurred with the utility’s finding.

“Data (in 2015) was totally lacking," said Akira Ishiwatari, an NRA commissioner who was in charge of the screening. "But after that a large volume of data was provided and upon reassessing all the information we found much data that led to the conclusion that no active fault existed.”

It took Hokuriku Electric more than eight years to come up with the data to deny the existence of an active fault because the initial method used did not provide the needed evidence.

A second method that required additional boring on the plant grounds finally led to the data the company needed.

But Hokuriku Electric is far from resuming operations at the No. 2 reactor because it must still pass screening of a number of measures to deal with possible tsunami or volcanic eruptions.

(This article was written by Takuro Yamano and Ryo Sasaki.)

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